This application relates to and incorporate herein by reference Japanese Patent Applications No. 8-336579 filed on Dec. 17, 1996, No. 8-344749 filed on Dec. 25, 1996 and No. 9-283208 filed on Oct. 16, 1997.
1. Field of the Invention
The present invention relates to a thermostat malfunction detecting system of an engine cooling system for detecting whether a thermostat for controlling the temperature of coolant of an engine is in malfunction or not.
2. Related Art
Generally, a thermostat which opens/closes in correspondence to the temperature of a coolant (cooling water) is provided in a coolant circulating path for circulating the coolant between a water jacket within an engine and a radiator in the water-cooled type engine. It is closed from the start of the engine until when the warm-up operation is completed to halt the circulation of the coolant to raise the temperature of the coolant quickly to the required temperature range and to improve the fuel consumption and to reduce noxious exhaust emission. The thermostat automatically opens when the temperature of the coolant on the engine side exceeds the required temperature range to circulate the low temperature coolant on the radiator side to the engine side to lower or maintain the temperature of the coolant on the engine side to the required temperature range.
As modes of malfunction of the thermostat, there are an open-malfunction during which the thermostat is kept opened and a closure-malfunction during which it is kept closed. When the open-malfunction occurs, the cold coolant within the radiator is circulated to the engine from the beginning of start even during the cold start time during which the engine is started while it is cold, so that the temperature of the coolant on the engine side is hampered from rising after the start, thus retarding the warm-up of the engine and increasing the fuel consumption and noxious exhaust emission. When the closure-malfunction occurs, the cold coolant on the radiator side is not circulated even when the temperature of the coolant on the engine side exceeds the required temperature range, so that there is a possibility that the temperature of the coolant on the engine side keeps rising, causing an over-heat of the engine in the end.
Thus, there has been a possibility that even when the thermostat has the open-malfunction, a driver continues to drive a vehicle without knowing it for a long period of time and continues to drive the vehicle until engine overheats when it has the closure-malfunction.
It is noted that there has been a technology of providing coolant temperature sensors at the inlet and outlet of the radiator, respectively, to evaluate the heat radiating performance of the radiator based on the temperature of coolant at the inlet and outlet of the radiator to detect the deterioration of the radiator as disclosed in Japanese Patent Application Laid-Open No. Hei. 4-19329. However, because the thermostat opens/closes automatically in correspondence to the temperature of the coolant on the engine side, the malfunction of the thermostat cannot be detected even if the coolant temperature on the radiator side which is not related to the opening/closing operation of the thermostat is detected at the two spots as disclosed. Still more, the cost becomes high because two temperature sensors have to be provided anew on the radiator side.
Accordingly, it is an object of the present invention to provide a thermostat malfunction detecting system of a cooling system of an internal combustion engine which detects the malfunction of the thermostat accurately at relatively low cost.
According to a first aspect of the present invention, a thermostat malfunction detecting system of detects, based on the behavior of a coolant temperature on the engine side, the coolant temperature on the path for circulating the coolant on the engine side from the thermostat (engine side coolant temperature) and diagnoses the thermostat whether it has an open-malfunction by which it is not closed and is kept opened (open-malfunction) based on the engine side coolant temperature detected in a temperature range in which the thermostat is normally closed. Because the behavior of the engine side coolant temperature is largely different during the normal time and during the open-malfunction in the temperature range in which the thermostat is normally closed, the thermostat may be diagnosed whether it has the open-malfunction accurately from the behavior of the engine side coolant temperature in this temperature range. Still more, because the coolant temperature may be detected by using the coolant temperature sensor for controlling the engine provided in the conventional engine, no new coolant temperature sensor needs to be added to the engine control system.
When a closure-malfunction by which the thermostat is not opened and is kept closed occurs, the thermostat is not opened, the coolant is not circulated and the engine side coolant temperature continues to rise up. Accordingly, the thermostat malfunction detecting system diagnoses the thermostat whether it has the closure-malfunction based on the detected engine side coolant temperature in the temperature range in which the thermostat is normally opened. Because the behavior of the engine side coolant temperature is largely different during the normal time and during the closure-malfunction in the temperature range in which the thermostat is normally opened, the thermostat may be diagnosed accurately whether it has the closure-malfunction from the behavior of the engine side coolant temperature in this temperature range.
According to a second aspect of the present invention, a thermostat malfunction detecting system detects the coolant temperature on the path for circulating the coolant on the engine side from the thermostat (engine side coolant temperature) as well as a coolant temperature on the path for circulating the coolant on the radiator side from the thermostat (radiator side coolant temperature) and diagnoses the thermostat whether it has a malfunction based on the engine side coolant temperature and the radiator side coolant temperature. Thereby, the malfunction of the thermostat can be detected accurately. Still more, because the engine side coolant temperature may be detected by using the coolant temperature sensor for controlling the engine which has been provided in the conventional engine and just a radiator side coolant temperature detecting means needs to be added anew to the engine control system, the structure can be relatively simple and the increase of the cost is minimized.
According to a third aspect of the present invention, a thermostat malfunction detecting system determines that the thermostat has a malfunction when a coolant temperature drops below a malfunction discriminating temperature which is lower than the thermostat closing temperature after when the coolant temperature reaches a warm-up completion temperature. That is, when the drop of the coolant temperature does not stop even if the coolant temperature drops below the thermostat closing temperature, it may be considered that the open-malfunction has occurred. Thereby, the open-malfunction of the thermostat may be detected by using the conventional coolant temperature sensor provided on the coolant circulating path of the engine and no new sensor or the like needs to be added, satisfying the demand on the reduction of the cost.